This invention relates to the one-step preparation of hexafluoroacetone by liquid phase reaction of hexafluorothioacetone dimer in an aprotic solvent containing alkali metal fluoride, at elevated temperature, with selected metallic and non-metallic oxides.
Hexafluoroacetone is a known compound useful as an intermediate in the preparation of hexafluoroisobutylene and hexafluoroisopropanol. Hexafluoroacetone also forms terpolymers with tetrafluoroethylene and with ethylene.
The preparation of hexafluorothioacetone dimer [2,2,4,4-tetrakis(trifluoromethyl)-1,3-dithietane] is disclosed by K. V. Martin in J. Chem. Soc., 2944 (1964). A mixture of hexafluorothioacetone dimer and hexafluorothioacetone monomer is produced by reacting hexafluoropropene with sulfur vapor over a carbon catalyst at 425.degree. C.; in the presence of a catalyst such as dimethylformamide, the monomer is converted into hexafluorothioacetone dimer.
In the presence of fluoride ion, a solution of hexafluorothioacetone dimer in dimethylformamide at ambient temperature is partially dissociated to produce an equilibrium mixture of monomeric and dimeric hexafluorothioacetone (T. Kitazume et al., Chemistry Letters, 267 (1973)).
The preparation of hexafluoroacetone by the gas phase oxidation of hexafluorothioacetone dimer with nitric oxide or sulfur dioxide in a Vycor tube packed with quartz heated to at 650.degree. C. is disclosed by W. J. Middleton and W. H. Sharkey in J. Org. Chem, Vol. 30, pages 1384-1390 (1965).
Hexafluoroacetone is also prepared (1) by high temperature gas phase fluorination of hexachloroacetone with HF in the presence of a chromium catalyst (L. G. Anello et al. in U.S. Pat. No. 3,257,457) and (2) by gas phase oxidation of hexafluoropropene with O.sub.2 in the presence of a fluorinated alumina catalyst (T. Touzuka et al. in U.S. Pat. No. 4,057,584).
These prior art preparations of hexafluoroacetone are effected in the gas phase with corrosive reactants such as HF over specially prepared catalysts such as chromium or fluorinated alumina or over quartz heated to 650.degree. C.
It is an object of the present invention to provide a process for liquid phase preparation of hexafluoroacetone from hexafluorothioacetone dimer. This and other objects and advantages will be apparent from the disclosure which follows.